Spring Make multiple slash sanitization optional in web util

Make multiple slash sanitization optional in UriComponentsBuilder and UrlPathHelper

No breaking changes introduced; users can continue using the default behavior without modification. Optional multi-slash sanitization is added to align with section 3.3 of RFC 3986, which permits empty path segments.

Closes gh-34076

Comment From: bclozel

Thanks for contributing to Spring Framework. Unfortunately, #34076 has been declined so I'll decline this PR as well.